Separately, the Republican said his party is "preparing our legal challenge" to ensure the prison remains open and detainees are not moved to the US.

Under MrObama's plan, roughly 35 of the 91 current prisoners will be transferred to other countries in the coming months, leaving up to 60 detainees who are either facing trial by military commission or have been determined to be too dangerous to release but are not facing charges.

Those detainees would be relocated to a US facility.

Mr Ryan said Mr Obama's plan flouts a long-standing ban annually passed by Congress that blocks the president from transferring Guantanamo detainees to US soil.

"If the president proceeds with knowingly breaking the law... he will be met with fierce bipartisan opposition here in Congress and we are taking all legal preparations necessary to meet with that resistance," Mr Ryan told reporters.

"He can't do it because the law is really clear. I'll just leave it at that."

Earlier this month, House Republicans awarded the Jones Day law firm with a 150,000 US dollars (£107,760) contract to perform the legal work in case Mr Obama tries to move Guantanamo detainees to federal prisons.

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